2.12 级联mock

出现obj1.getObj2(...).getYetAnotherObj().doSomething(...)时可能需要mock多个对象。对于一个mock对象:

• Expectation中进行了record，则会返回record的result；
• 如果没有record，JMockit会自动创建一个返回被注解@Injectable的子对象

public class Dependency {

    public CascadeDependency getCascadeDependency() {
        //JMockit会拦截这个方法，返回一个非null对象
        return null;
    }
    
    public CascadeDependency getAnotherCascadeDependency() {
        //JMockit会拦截这个方法，返回一个非null对象
        return null;
    }

    public String getString() {
        //仍旧返回null
        return null;
    }

    public Object getObject() {
        //仍旧返回null
        return null;
    }

    public List<Object> getList() {
        //返回empty集合
        return null;
    }
}

@Test
public void TestMethod(@Mocked Dependency dependency) {

    CascadeDependency first = dependency.getCascadeDependency();
    CascadeDependency second = dependency.getCascadeDependency();
    
    //调用另一个方法
    CascadeDependency third = dependency.getAnotherCascadeDependency();
    
    //所有都不会为null
    assertNotNull(first);
    assertNotNull(second);
    assertNotNull(third);
    
    //相同方法返回JMockit创建的同一个对象
    assertSame(first, second);
    
    //不同方法返回JMockit创建的同一个对象
    assertNotSame(first, third);
    
    //String返回null
    assertNull(dependency.getString());

    //Object返回null
    assertNull(dependency.getObject());
    
    //返回empty集合
    assertNotNull(dependency.getList());
    assertEquals(0, dependency.getList().size());
}

@Test
public void TestMethod(@Mocked Dependency dependency， 
                       @Mocked CascadeDependency cascadeDependency) {

    CascadeDependency first = dependency.getCascadeDependency();
    CascadeDependency second = dependency.getAnotherCascadeDependency();
    
    //因为子对象也@Mocked，所以会返回同一个对象
    assertSame(first, second);
}

JMockit返回的非空对象实际上进行了@Injectable标识，所以：

@Test
public void TestMethod(@Mocked Dependency dependency) {

    //虽然CascadeDependency没有出现在参数中，
    //但是JMockit对其进行了@Injectable
    //而由于没有在Expectation中record mockMethod的result，所以返回空
    assertNull(dependency.getCascadeDependency().mockMethod());

    //不影响CascadeDependency的其他实例
    assertNotNull(new CascadeDependency().mockMethod());
}

也可以在Expectation中使用result指定返回对象，从而禁止JMockit自动生成。

@Test
public void TestMethod(@Mocked final Dependency dependency) {

    //在Expectation中指定了返回结果，因此JMockit不会生成CascadeDependency
    new NonStrictExpectations(){{
        dependency.getCascadeDependency();
        result = null;
        result = new CascadeDependency();
    }};
    
    //第一次返回null
    assertNull(dependency.getCascadeDependency());
    
    //第二次返回新对象
    assertNotNull(dependency.getCascadeDependency().mockMethod());
}

mock级联调用特别适合static factory，getCurrentInstance()永远不会返回null。

@Test
public void TestMethod(@Mocked final Dependency dependency) {
    assertSame(dependency, dependency.getCurrentInstance());
}

在Builder模式中也很方便验证，

@Test
public void createOSProcessToCopyTempFiles(@Mocked final ProcessBuilder pb) throws Exception{
    Process copy = new ProcessBuilder().command(cmdLine).directory(wrkDir).inheritIO().start();

   new Verifications() {{ pb.command(withSubstring("copy")).start(); }};
}